Multi-tasking and the Cell Phone

Why is it that we can be involved in one thing with a group of people or a person and still be on our cell phones? What did we ever do before cell phones? I think that if you are talking to people use common sense and only hold one conversation at a time. It still comes off as rude. If you were with more than one person you wouldn't hold two different conversations at the same time, so you shouldn't do it with your cell phone either. I can understand if you had an emergency and needed to know something. We have become a society though that is involved in ourselves and forgetful about others feelings. It does not make people feel good and makes them feel disrespected when you are involved in something on your cell and don't even acknowledge others that are right in front of you.